The present invention relates to a drive unit for a model helicopter according to the preamble of the main claim.
In detail, the invention relates to a drive unit for a model helicopter comprising a fuselage the central portion of which has formed thereon bearing points for the detachable attachment of a carrier for supporting a rotor shaft, a transmission and a drive.
Very different designs of drive units for model helicopters are known from model construction. These normally comprise model engines based on the two-stroke combustion principle, as are also used in fixed-wing airplane models.
It is desired in model-making and, in particular, in airplane and helicopter model construction, that the models are as realistic as possible not only optically but also with respect to their operability. That is why it has always been found to be a disadvantage when internal combustion engines of a standard construction are installed in helicopter models. Piston engines produce a very typical sound which differs from that of the original examples operated with turbines. In addition, the exhaust generation in two-stroke engines is not realistic. This is also true for airplane models of jet engine airplanes which have the additional flaw that propellers must be provided that impair their appearance quite considerably.
That is why attempts have recently been made to build miniature turbines which both in their form and their noise generation and also with respect to their exhaust characteristics correspond to original turbines and jet engines, respectively. The installation of such miniature turbines in fixed-wing airplanes does not present any problems because the original examples can be followed.
By contrast, it is not possible to install miniature turbines in helicopter models of a standard size because both the installation position and transmission arrangements cannot be exactly copied on a reduced scale. In addition, it is difficult to imitate adequate air intake openings and exhaust openings of the original design because the model turbines, based on the scale of such helicopters, are not small enough.
On the other hand it has so far not been possible to provide transmission assemblies suited for a model drive.
It is the object of the present invention to provide a drive unit for a model helicopter of the above-mentioned type which, using a turbine and being of a simple construction and reliable operability, can be used in a model helicopter.
According to the invention this object is achieved by the features of the main claim; the subclaims show further advantages arising from the design of the invention.
The drive unit according to the invention is characterized by a number of considerable advantages.
Thanks to the horizontal arrangement of the turbine it is possible on the one hand to adapt the direction of flow of the turbine of the model helicopter to the original examples of helicopters and, in particular, to design the fuselage true to scale. This applies, in particular, to the inlet portion and the air supply to the turbine.
Thanks to the extended design of the turbine shaft in the inlet portion it is possible in a particularly easy manner to support the turbine in an operationally safe manner and to transmit the output power to the transmission. At the same time the air inflow to the turbine effects an efficient cooling of the transmission.
It is of particular advantage that the turbine shaft is supported on a carrier which carries the transmission. As a result, a safe assignment between turbine and transmission is ensured.
The turbine shaft is preferably supported on the carrier by means of a pre-loaded bearing. Advantageously, the bearing is mounted on the free end portion of the turbine shaft so that the transmission can be flanged to the area of the turbine shaft positioned behind the bearing. This measure enhances the overall stability of the arrangement.
Both for reasons of an optimum center-of-gravity position and for diverting the exhaust gases in an advantageous manner, it is intended that the turbine is installed in the direction of flow behind the rotor shaft.
According to the invention the transmission is preferably of a three-stage configuration; it can be designed as a belt transmission, as a toothed gearing or as a friction gear.
Preferably, the transmission has a gear reduction of 100,000 rpm to 1,200 to 1,800 rpm.
A clutch is preferably arranged between the transmission and the rotor shaft so as to separate the transmission and the rotor, in particular in case of transmission or turbine failures. In such a case the model helicopter can land safely by autorotation of the rotor.
It is particularly advantageous when the turbine is provided with a speed limiter. The limiter may e.g. comprise a control means for a fuel pump.